The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
This disclosure relates to compositions and methods for removing non-aqueous fluids from a subterranean wellbore.
During the construction of subterranean wells, it is common, during and after drilling, to place a tubular body in the wellbore. The tubular body may comprise drillpipe, casing, liner, coiled tubing or combinations thereof. The purpose of the tubular body is to act as a conduit through which desirable fluids from the well may travel and be collected. The tubular body is normally secured in the well by a cement sheath. The cement sheath provides mechanical support and hydraulic isolation between the zones or layers that the well penetrates. The latter function is important because it prevents hydraulic communication between zones that may result in contamination. For example, the cement sheath blocks fluids from oil or gas zones from entering the water table and polluting drinking water. In addition, to optimize a well's production efficiency, it may be desirable to isolate, for example, a gas-producing zone from an oil-producing zone. The cement sheath achieves hydraulic isolation because of its low permeability. In addition, intimate bonding between the cement sheath and both the tubular body and borehole is necessary to prevent leaks.
The cement sheath is usually placed in the annular region between the outside of the tubular body and the subterranean borehole wall by pumping the cement slurry down the interior of the tubular body, out the bottom and up into the annulus. The cement slurry may also be placed by the “reverse cementing” method, whereby the slurry is pumped directly down into the annular space. During the cementing process, the cement slurry is frequently preceded by a spacer fluid or chemical wash to prevent commingling with drilling fluid in the wellbore. These fluids also help clean the tubular-body and formation surfaces, promoting better cement bonding and zonal isolation. The cement slurry may also be followed by a displacement fluid such as water or a brine. This fluid usually resides inside the tubular body after the cementing process is complete. A complete description of the cementing process and the use of spacer fluids and chemical washes is presented in the following publications. Piot B and Cuvillier G: “Primary Cementing Techniques,” in Nelson E B and Guillot D: Well Cementing-2nd Edition, Houston, Schlumberger (2006) 459-501. Daccord G, Guillot D and Nilsson F: “Mud Removal,” in in Nelson E B and Guillot D: Well Cementing-2nd Edition, Houston, Schlumberger (2006) 143-189.
Drilling-fluid removal and wellbore cleaning may be challenging when the well has been drilled with non-aqueous fluids. In the art of well cementing, non-aqueous fluids may be oil-base muds or water-in-oil emulsions. Conventionally, operators employ water-base spacer fluids or chemical washes comprising surfactants that render the fluids compatible with non-aqueous fluids. In the context of well cementing, fluids are compatible when no negative rheological effects such as gelation occur upon their commingling. Such effects may hinder proper fluid displacement, leaving gelled fluid in the wellbore and reducing the likelihood of achieving proper zonal isolation. Ideally, the spacer fluid, chemical wash or both will completely remove the non-aqueous fluid and leave casing and formation surfaces in the annulus water wet. Water-wet surfaces may promote intimate bonding between the cement sheath and casing and formation surfaces.
Many of the surfactants commonly used in the art to impart compatibility of spacer fluids and chemical washes with non-aqueous fluids may not be suitable for use in regions where governmental regulations restrict their use, disposal, or both. Therefore, despite the valuable contributions of the prior art, it remains desirable to have materials and methods by which non-aqueous fluids may be removed from a wellbore, yet comply with governmental regulations.